Hip stem prosthesis with a porous collar to allow for bone ingrowth

ABSTRACT

A femoral hip implant includes a first end, a second end, and a collar with a porous surface, all fabricated from a single piece of material. The entire area of the collar is porous, and the collar elastically deflects under load to promote bone ingrowth.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/697,177, which was filed on Sep. 5, 2012, and U.S. ProvisionalApplication No. 61/790,528, which was filed on Mar. 15, 2013, both ofwhich are incorporated herein by reference in their entirety.

FIELD

The present disclosure relates to embodiments of a femoral hip implant.

BACKGROUND

There are two primary methods of fixation for femoral hip implants intotal hip replacement. The first method utilizes bone cement to bond thefemoral hip implant to the surrounding bone. The second method relies ona press fit between the femoral hip implant and the bone to promote longterm stability. Such press fit implants are commonly tapered to resistpost-operative subsidence into the bone canal, and can include poroussurfaces to promote bone ingrowth. Many press fit implants also includea collar that rests on the calcar area of the femur, acting to restrainsubsidence and allow load sharing between the bone and the implant.

SUMMARY

In some embodiments, a bone implant apparatus is provided. The apparatuscomprises a first end having a substantially smooth surface to inhibitbone ingrowth, a second end extending from the first end in anon-coaxial fashion with a tapered shape and a surface, at least aportion of which comprises a porous surface to allow bone ingrowth, anda collar located between the first and second end. The collar furthercomprises a porous surface to allow bone ingrowth into the collar.

In some implementations, a femoral hip implant is provided comprising afirst end, the first end having a substantially smooth surface toinhibit bone ingrowth, a second end having a substantially tapered shapeand extending from the first end in a non-coaxial fashion, at least aportion of which comprises a porous surface to allow bone ingrowth, anda collar located between the first end and the second end, at least aportion of the collar having a porous surface to allow bone ingrowth.The second end of the femoral hip implant is inserted into a femur, andthe femoral hip implant is positioned to subside into the femur untilthe collar contacts the femur so that the porous surfaces of the secondend and the collar are aligned with bone to allow bone ingrowth.

The foregoing and other objects, features, and advantages of theinvention will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a femoral hip implant.

FIG. 2 is an enlarged isometric view of a femoral hip implant.

FIG. 3 is a cross-sectional view of a femoral hip implant in a femur.

FIG. 4A is a front view showing a hip joint before total hipreplacement.

FIG. 4B is a front view of a femoral hip implant showing a gap between afemur and a collar.

FIG. 4C is a front view of a femoral hip implant showing a collar incontact with a femur.

FIG. 4D is a magnified view of FIG. 4B.

FIG. 4E is a magnified view of FIG. 4C.

FIG. 5 is a representation of the geometric pattern of a porous surface.

FIG. 6 is a micrograph of the geometric pattern of a porous surface.

FIG. 7 is a front view of a diamond cubic unit cell geometry of a poroussurface of a femoral hip implant.

FIG. 8 is a diagram showing cross-section of a collar and application ofa force to the collar.

FIG. 9 is a diagram showing the deflection of a collar under load.

FIG. 10 is a side elevation view of a femoral hip implant having analternative embodiment of a collar.

FIG. 11 is a side elevation view of the femoral hip implant of FIG. 1illustrating a length of the collar.

FIG. 12 is a side elevation view of the femoral hip implant of FIG. 10illustrating a length of the collar.

FIG. 13 is a side elevation view of another embodiment of a femoral hipimplant.

FIG. 14 is an enlarged isometric view of a portion of the femoral hipimplant of FIG. 13.

DETAILED DESCRIPTION

For purposes of this description, certain aspects, advantages, and novelfeatures of the embodiments of this disclosure are described herein. Thedisclosed methods, apparatuses, and systems should not be construed aslimiting in any way. Instead, the present disclosure is directed towardall novel and nonobvious features and aspects of the various disclosedembodiments, alone and in various combinations and sub-combinations withone another. The methods, apparatus, and systems are not limited to anyspecific aspect or feature or combination thereof, nor do the disclosedembodiments require that any one or more specific advantages be presentor problems be solved.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed methods can be used in conjunction with other methods.Additionally, the description sometimes uses terms like “provide” or“achieve” to describe the disclosed methods. These terms are high-levelabstractions of the actual operations that are performed. The actualoperations that correspond to these terms may vary depending on theparticular implementation and are readily discernible by one of ordinaryskill in the art.

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the terms “coupled” and “associated” generally meanelectrically, electromagnetically, and/or physically (e.g., mechanicallyor chemically) coupled or linked and does not exclude the presence ofintermediate elements between the coupled or associated items absentspecific contrary language.

As used herein, the term “porous” means a structure having one or moreopenings, gaps, or other such surfaces that allow bone to grow into thestructure and mechanically interlock with the structure. “Bone ingrowth”refers to the growing of bone into a porous structure in a manner thatallows the bone to interlock with the structure.

As used herein, the term “smooth” means a structure lacking in openings,gaps, or other such surfaces that would allow bone to grow into thestructure.

A collar with a porous surface acts to stabilize a femoral hip implantby promoting bone ingrowth. However, due to manufacturing limitations,the existing art implants often comprise a solid metal collar with onlya textured undersurface. Such textured undersurfaces are ineffective atpromoting bone ingrowth, and frequently cause bone resorption under thecollar instead. Such bone resorption in turn can cause the femoral hipimplant to loosen in some cases, and can result in undesirable revisionsurgery.

FIGS. 1-2 depict an embodiment of a femoral hip implant 10. Femoral hipimplant 10 comprises a first end 12 (e.g., a proximal portion) having asubstantially smooth surface, a second end 14 (e.g., a distal portion)extending distally from the first end 12 in a non-coaxial fashion, and acollar 16 positioned between the first end 12 and the second end 14. Insome embodiments, the first end 12 is adapted to receive a femoral head(not shown) and the second end 14 has a tapered shape generallycomprising a femoral stem and a porous region 18. In some embodiments,first end 12, second end 14, and the collar 16 are integrally formedfrom a single piece of material. Additionally, the femoral hip implant10 can be configured for both human and veterinary applications.

The collar 16 can comprise a substantially semicircular projection fromsecond end 14 generally normal to the second end 14, as shown in FIGS.1-2. In this configuration, the collar 16 can contact the hard calcararea 20 of the femur 22, as shown in FIGS. 3 and 4E, allowing thefemoral hip implant 10 to transfer force to the bone when loaded.Additionally, the collar 16 can prevent the femoral hip implant 10 fromsubsiding into the femur 22 by contacting the calcar area 20 of thefemur 22 to arrest motion of the femoral hip implant 10 into the bonecanal.

Collar 16 can comprise a top surface 24 and a bottom surface 26, asshown in FIGS. 1-2. In some cases, the bottom surface 26 of the collar16 will not contact the calcar area 20 of the femur 22 when the femoralhip implant 10 is first implanted. Rather, the femoral hip implant 10will generally achieve a sufficiently tight press fit before it impactsinto the femur 22 far enough to allow the bottom surface 26 of thecollar 16 to contact the calcar area 20, as shown in FIG. 4D. However,in some cases, the tightness of the original press fit can decreasepost-operatively, allowing the femoral hip implant 10 to subside furtherinto the femur 22 and causing collar 16 to make contact with the calcararea 20 of the femur 22, as shown in FIG. 4E. This action arrestsfurther subsidence of the femoral hip implant 10 into the femur 22 andaligns the porous surfaces of the second end and the collar with bone tofacilitate bone ingrowth.

In some embodiments, the collar 16 can be fully porous, with the entiresurface area of the collar 16 exhibiting porosity as shown in FIGS. 1-2.Porous surfaces exhibiting proper geometry can promote bone ingrowth,creating mechanical interlocking between the bone and the femoral hipimplant 10. Such bone ingrowth improves the long term stability of theimplant by reducing stress concentrations and bone resorption, as wellas improving the torsional strength of the implant and reducing thelikelihood of the need for revision surgery.

In some embodiments, the top surface 24 of the collar 16 can comprise asolid (i.e., non-porous) metal surface or skin. The solid metal surfacecan be from about 0.005 inches to about 0.025 inches thick, and canfurther strengthen the collar 16. In other embodiments, the thickness ofthe metal at top surface 24 (the surface facing away from the femur 22)can vary between between 0.005 inches to 0.08 inches thick, or morepreferably between 0.01 to 0.06 inches thick. An embodiment with the topsurface 24 being formed with a metal surface (e.g., a thin metal “skin”)is shown in FIGS. 12 and 13. All of the side of the collar 16 can beformed with a porous surface as shown in FIG. 1; alternatively, all orsome of the side of the collar 16 can be formed with a non-porous metalsurface as shown in FIG. 14. In either embodiment (FIG. 1; FIG. 12), thelower surface (i.e., the bone-contacting surface as shown in FIG. 3) ofcollar 16 is preferably formed with a porous surface that can promotebone ingrowth as discussed above.

In some embodiments, the length L₁ of the collar 16 can be related to across-sectional dimension D of the second end 14, as shown in FIG. 11.The length L₁ of the collar 16 can be from about 12% to about 26% of thecross-sectional dimension D of the second end 14. In some embodiments,the length L₁ of the collar 16 can be about 26% of the dimension D ofthe second end.

The femoral hip implant 10 described herein can be formed of variousbiocompatible materials. In some embodiments, the femoral hip implant 10can be formed of titanium alloys, such as ASTM F-136 (Ti6Al4V ELITitanium Alloy). In other embodiments, the implants can be formed usingother biocompatible materials, such as cobalt chromium, stainless steel,and various composite materials or plastics.

Existing art implants require that the implant comprise multiple partsjoined together to achieve a porous surface on both the collar andtapered body of the implant. However, using additive machiningtechniques such as electron beam melting (EBM) or laser sintering, thefemoral hip implant 10 can be made from a single piece of material. Inthe case of the EBM technique, the implant can be produced by buildingthe implant layer-by-layer from metal powder (e.g., a titanium alloypowder) using a powerful electron beam. In the case of the lasersintering technique, a high-powered laser is used to fuse beads ofmaterial to form the desired three-dimensional structure. Thesetechniques can be used to produce an implant with the desired poroussurfaces, allowing the porous surface of the femoral hip implant 10 toextend from the porous region 28 of the second end 14 to cover theentire surface area of the collar 16, as shown in FIGS. 1-2.

The porosity of the femoral hip implant 10 is generally of a diamondcubic unit cell geometry, as shown in FIGS. 5-6, although any geometrycreating a three-dimensional structure of sufficient porosity to allowbone ingrowth may be used. In some embodiments, the diamond cubic unitcell geometry comprises a 7-14 diamond cubic unit cell structure withapproximately sixty-five percent of the interior volume comprising spaceand thirty-five percent comprising solid material. Although any ratio ofspace to solid material may be used, in some embodiments this ratio cancomprise a majority of space as compared to solid material. In someembodiments, the diameter of the diamond unit cell structure isapproximately 300 μm and the height is approximately 350 μm, with a poresize ranging from approximately 350-700 μm, as shown in FIG. 7. In someembodiments, the thickness is approximately 1000 μm, although anyeffective thickness may be used. Porosity of this size promotes boneingrowth with sufficient vascularity to the underlying bone withoutcompromising the structural integrity of the collar 16 under load.

An additional feature of the collar 16 is its greater ability toelastically deflect under load compared to existing art solid collarswith porous or textured surface treatments. The porosity of the collar16 increases the elastic deflection of the collar 16 when subjected toloading by reducing the ultimate strength of the collar 16. Existing artcollars fabricated from ASTM F-136 (Ti6Al4V ELI Titanium Alloy) withcross-sections of 0.310 inches by 0.120 inches exhibit an ultimatematerial stress of approximately 138,000 pounds per square inch with afracture force of approximately 466 pounds. Such existing art solidcollars generally are too stiff to deflect under normal loadingconditions induced in femoral implants, leading to stress disuse boneresorption in the calcar area and destabilization of the implant.However, in some embodiments of the femoral hip implant 10, the collar16 exhibits an ultimate material stress of approximately 48,000 poundsper square inch and a fracture load of approximately 163 pounds with across-section of 0.310 inches by 0.120 inches, as shown in FIG. 8. Thisreduction in the ultimate material stress and fracture force caused bythe porosity of collar 16 in turn causes increased elastic deflection ofcollar 16 under load. As can be seen in FIG. 9, elastic deflection ofcollar 16 ranges from less than 0.004 inches to nearly 0.020 inches as aload ranging from 0 pounds to 188 pounds is applied. This elasticdeflection of collar 16 can stimulate bone regeneration around collar16, promoting bone ingrowth and long-term stabilization of the femoralhip implant 10.

Referring now to FIG. 10, there is shown an alternative embodiment of acollar 116. The collar 116 can have a top surface 124 and a bottomsurface 126, and can be positioned between the first and second ends 12,14 of the implant 10, similar to the collar 16 of FIG. 1. The collar 116can also have an entirely porous surface to promote bone ingrowth. Asshown in FIG. 10, the bottom surface 126 of the collar 116 can form anangle α with a longitudinal axis of the implant. In some embodiments,the angle α can be from about 45 degrees to about 130 degrees. In someembodiments, the angle α can be about 110 degrees, and the collar 116can have a generally tapered shape corresponding to the angle α. In thismanner, the bending stress experienced by the collar 116 in use can befurther reduced.

In some embodiments, the top surface 124 of the collar 116 can comprisea solid (i.e., non-porous) metal surface similar to the solid metalsurface discussed above with respect to the embodiment of FIG. 1. Insome embodiments, the length L₂ of the collar 116 can be related to thecross-sectional dimension D of the second end 14, as shown in FIG. 12.The length L₂ of the collar 116 can be from about 12% to about 26% ofthe cross-sectional dimension D of the second end 14, similar to thecollar of FIG. 1. In some embodiments, the length L₂ of the collar 16can be about 12% of the dimension D of the second end, as shown in FIG.12. In this manner, the bending stress experienced by the collar 116 inuse can be further reduced.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. I thereforeclaim as my invention all that comes within the scope and spirit ofthese claims.

I claim:
 1. A bone implant apparatus comprising: a first end having asubstantially smooth surface to inhibit bone ingrowth; a second endextending from the first end in a non-coaxial fashion, the second endhaving a tapered shape and a surface, at least a portion of whichcomprises a porous surface to allow bone ingrowth; and a collar locatedbetween the first end and the second end, the collar comprising asurface at least a portion of which comprises a porous surface to allowbone ingrowth into the collar.
 2. The bone implant apparatus of claim 1,wherein the first end, the second end, and the collar comprise a singlepiece of material.
 3. The bone implant apparatus of claim 1, wherein theentire surface area of the collar is porous.
 4. The bone implantapparatus of claim 1, wherein the collar further comprises a top surfaceand a bottom surface, both of which are porous.
 5. The bone implantapparatus of claim 4, wherein the top surface and the bottom surface ofthe collar are generally parallel.
 6. The bone implant apparatus ofclaim 4, wherein the portion of the surface of the second end comprisinga porous surface extends along the top surface and the bottom surface ofthe collar.
 7. The bone implant apparatus of claim 4, wherein the bottomsurface of the collar forms an angle with a longitudinal axis of thebone implant apparatus of from about 45 degrees to about 130 degrees. 8.The bone implant apparatus of claim 7, wherein the bottom surface of thecollar forms an angle with the longitudinal axis of the bone implantapparatus of about 110 degrees.
 9. The bone implant apparatus of claim1, wherein the collar comprises a substantially semicircular projectionfrom the second end of the bone implant apparatus in a directionsubstantially normal to the second end.
 10. The bone implant apparatusof claim 1, wherein at least a portion of the surface of the boneimplant apparatus comprises a substantially smooth surface thatrestricts bone ingrowth.
 11. The bone implant apparatus of claim 1,wherein the collar elastically deflects under load to stimulate bonegrowth.
 12. The bone implant apparatus of claim 11, wherein the elasticdeflection of the collar is between 0.004 inches and 0.02 inches whensubjected to a load of 188 pounds.
 13. The bone implant apparatus ofclaim 11, wherein the elastic deflection of the collar is greater than0.004 inches when subjected to a load of 188 pounds.
 14. The boneimplant apparatus of claim 1, wherein the porous surfaces of the secondend and the collar comprise a diamond cubic unit cell geometry.
 15. Thebone implant apparatus of claim 1, wherein the bone implant apparatus isfabricated from a biocompatible material.
 16. The bone implant apparatusof claim 1, wherein the collar comprises a non-porous metal surface witha thickness of from about 0.005 inches to about 0.025 inches.
 17. Thebone implant apparatus of claim 1, wherein the collar has a length offrom about 12% to about 26% of a cross-sectional dimension of the secondend of the implant.
 18. A method for total hip replacement, comprising:providing a femoral hip implant comprising a first end, the first endhaving a substantially smooth surface to inhibit bone ingrowth, a secondend having a substantially tapered shape and extending from the firstend in a non-coaxial fashion, at least a portion of which comprises aporous surface to allow bone ingrowth, and a collar located between thefirst end and the second end, at least a portion of the collar having aporous surface to allow bone ingrowth; inserting the second end of thefemoral hip implant into a femur; and positioning the femoral hipimplant to subside into the femur until the collar contacts the femur sothat the porous surfaces of the second end and the collar are alignedwith bone to allow bone ingrowth.
 19. The method of claim 18, whereinthe collar of the femoral hip implant elastically deflects upon loadingand unloading of the femoral hip implant.
 20. The method of claim 19,wherein the elastic deflection of the collar is between 0.004 inches and0.02 inches when subjected to a load of 188 pounds.
 21. The method ofclaim 19, wherein the elastic deflection of the collar is greater than0.004 inches when subjected to a load of 188 pounds.
 22. The method ofclaim 18, wherein the inserting of the femoral hip implant into thefemur comprises press-fitting the femoral hip implant into the femur.23. The method of claim 18, wherein the first end, the second end, andthe collar of the femoral hip implant comprise a single piece ofmaterial.
 24. The method of claim 18, wherein the collar comprises asubstantially semicircular projection from the second end of the femoralhip implant in a direction generally normal to the second end of thefemoral hip implant.
 25. The method of claim 18, wherein the entiresurface area of the collar comprises a porous surface.
 26. The method ofclaim 18, wherein the porous surfaces of the second end and the collarcomprise a diamond cubic unit cell geometry.
 27. The method of claim 18,wherein the bone implant apparatus is fabricated from a biocompatiblematerial.
 28. A bone implant comprising: a proximal portion adapted forreceiving a femoral head, the proximal portion being fabricated from abiocompatible material; a distal portion having a generally taperedshape and extending distally from the proximal portion in a non-coaxialfashion, the distal portion comprising a femoral stem configured forpress-fit insertion into a femur without the use of bone cement, thedistal portion comprising a surface at least a portion of which isporous, the porosity of the porous surface of the distal portioncomprising a diamond cubic unit cell geometry to allow bone ingrowth,the distal portion and the proximal portion comprising a single piece ofmaterial, the distal portion being fabricated from a biocompatiblematerial; a collar, the entire surface area of which is porous, thecollar being generally disposed between the proximal portion and thedistal portion, the collar being generally disposed about a proximal endof the distal portion, the collar comprising a generally semicircularprojection, the collar comprising a top surface and a bottom surface,both of which are porous, the top surface and bottom surface beinggenerally parallel, the porous surface of the collar integrallyextending onto the surface of the distal portion, the porosity of thecollar comprising a diamond cubic unit cell geometry to allow boneingrowth, the collar elastically deflecting more than 0.004 inches undera load of 188 pounds, the collar, the proximal portion, and distalportion comprising a single piece of material, and the collar beingfabricated from a biocompatible material.